2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/43603Under assumption of singular behavior of alpha_s(q^2) at q^2 sim 0 and of large q^2 behavior, corresponding to the perturbation theory up to four loops, a procedure is considered of matching the beta-function at a boundary of perturbative and non-perturbative regions. The contribution of the non-perturbative region to the gluon condensate is calculated with varying normalization condition alpha_s(m_tau^2) = 0.29, 0.30,..., 0.36 for two different ways of definition of the non-perturbative invariant charge in the infrared region. We obtain quite consistent results for values of the gluon condensate, nonperturbative region scale q_0, and the string tension sigma.LaTeX, 10 pages, 2 figures, added reference, not great elucidation after eq.(3) and in abstractHigh Energy Physics - Phenomenologytext